Without providing context, asking a question like this does indeed sound like you are doing homework, in which no one is going to do your work for you. Why don't you tell us what you are trying to accomplish, or what caused you to ask this question and we might be able help. It also helps if you tell us what research you have already done.

Ted Aside from the fact that it looks like you're asking other people to do your home the other reason for the reaction is that you're asking a very elementary level question, and equivalent of which is like going onto a IT forum and asking "what is a computer?", you should google search you will find tonnes of articles, however you will need to use context to narrow down the search critera to find the information you're looking for.